1. Field of the Invention
The present invention relates to a display device for allowing a viewer to see a real image of an observed object formed in the air by using an imaging optical system of real specular image.
2. Description of the Related Art
There has been developed a display device using a microlens-array which can visually provide a real image of an observed object such as a displayed image floating in the air to a viewer, for example (see Japanese Published Unexamined Patent Application No. 2001-255493). This display device uses an optical system of an erect equal magnification for a two dimensional image in which spatially parallel translation of the two dimensional image is realized by a display surface displaying a two dimensional image and an optical device having the same size of the display surface so as to optically make a displayed image in the air without distortion. Such configuration is useful for the optical device to come down in size and thickness in comparison with that using a normal lens, so that it contributes to compact the display device. However, even by such a display device, an actual real image of a three dimensional image is not obtained although the two dimensional real image like a stereoscopic image is obtained. Furthermore, since a viewer looks at the real image of refraction of light imaged by the microlens-array in such a display device, the viewer see the image only in the front of the microlens-array.
Whereas there has been developed a display device using an imaging optical system of real specular image (for example, see the international publication No. WO2007-116639) in which a micromirror array (configured with a plurality of dihedral corner reflectors each of which is composed of two specular surfaces being orthogonal to each other) is utilized so that a two dimensional image or three dimensional object to be projected alternatively a displayed image is observable in the air as a real specular image (real image). By the dihedral corner reflectors, the real image of the observed object is imaged at a position of plane symmetry with respect to the element surface (as plane of symmetry) without distortion. A display device using such dihedral corner reflectors allows a viewer to observe a two dimensional real image caused by a two dimensional object (or a three dimensional real image caused by a three dimensional object) from a viewpoint in an oblique direction in a space opposite to the observed object with respect to the element surface. In other words, the imaging optical system of real specular image is an imaging optical system partitioning a space in which the viewer exists (viewer-side space) off the space opposite to the viewer-side space (object-side space in which the object is placed) to image a real image of the observed object in the viewer-side space, while including a plane of symmetry between the observed object and the real image.
There is suggested a display device capable of displaying a real image of the observed object as a floating image in the front of the display surface of devices such as the instrument panel such as a meter cluster, namely viewer-side space, using the imaging optical system of real specular image allowing observation of areal image of the observed object from a viewpoint in an oblique direction with respect to the element surface (see Japanese Published Unexamined Patent Application No. 2009-223232). This publication of JP2009-223232 discloses an example in that, the real image of a displayed image on the display surface of an electronic display device (adapted as an observed object) is imaged in a space, in which nothing is originally expected to exist, in the front of the instrument panel at which a driver (viewer) looks while driving an automobile so that the floating attractive image may awaken attention of the viewer.
In case that the display device disclosed by the foregoing JP2009-223232 is adapted to the automobile, for example, there is seen in the driver's sightline direction both the displayed instrument panel and the floating image in the front thereof in the air, furthermore, such an image may be imaged to be moving so as to attract attention of the viewer. There is a demand to a display device capable of giving the driver the larger quantity of more impressive information.